The long-term objective of this study is to understand the neural circuitry underlying emotional behavior in primates. The proposed experiments focus on the transynaptic circuitry of the amygdala, a structure in the medial temporal lobe that is important for emotion, and in humans has been linked with clinical disorders such as affective illness, anxiety, autism, and schizophrenia. Our understanding of the mechanisms underlying these disorders relies in great part on our ability to understand the precise flow of information through the amygdala and neuroanatomically related regions. The organization of monosynaptic connections within the primate amygdala has been identified in great part in previous studies. However, because of the complexity of intrinsic amygdala connections and because of the limitations of classic neuronal tracers, it has been extremely difficult to identify the multisynaptic pathways, or the functional flow of information, through the amygdala. The present study will apply the use of a new class of transneuronal tracers, live neurotropic viruses, to identify chains of synaptic connections within the primate amygdala. The viral tracing method will be developed in the context of one specific research question with the goal of applying this to future, larger scale studies of amygdala circuitry. The specific aim of the present study is to identify the functional pathway(s) between two nuclei of the amygdala, the lateral nucleus, a major recipient of cortical inputs to the amygdala, and the central nucleus, one of the major output nuclei of the amygdala. These studies will reveal whether information flow from the lateral nucleus to the central nucleus involves only a monosynaptic connection or whether two or more synapses are involved. This will not only provide valuable data on the circuitry of the amygdala, but will provide the scientific community with a new methodology to more broadly understand information flow through the amygdala. Understanding the functional organization of the amygdala is a crucial step towards the ultimate goal of this research program: to obtain information that will aid in the treatment of neurological and psychiatric disorders of emotion caused by trauma, disease, and developmental defects. This goal is pertinent to a variety of clinical applications, including the development of pharmacological and behavioral treatment programs for patients who suffer with emotional disorders.